Primary Biliary Cirrhosis (cont.)
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Xanthomas
Cholesterol may deposit in the skin around the eyes or in skin creases of the
palms, soles, elbows, knees, or buttocks. Collectively, these waxy, raised
deposits are called xanthomas. Such deposits around the eyes are also referred
to as xanthalasma. Xanthomas are more common in PBC than in any other liver
diseases associated with cholestasis. Most xanthomas do not cause symptoms, but
those on the palms sometimes can be painful. Rarely, xanthomas deposit in nerves
and cause a neuropathy (disease of the nerve). This neuropathy is characterized
by abnormal sensation in the parts of the body, most often the limbs, supplied
by the affected nerves.
Although elevated levels of cholesterol in the blood are common in PBC and
other liver diseases with cholestasis, xanthomas are found in only 25% of
patients at the time of diagnosis. Xanthomas tend not to occur until the serum
cholesterol rises to very high levels, for example, above 600 mg/dL. Xanthomas
tend to spontaneously disappear in patients with advanced liver disease due to
impaired production of cholesterol by the damaged liver. Importantly, the high
levels of serum cholesterol in PBC do not seem to increase the risk of heart
disease because the composition of the cholesterol is different from the usual
cholesterol (atypical) and does not easily deposit in blood vessels.
Malabsorption of fat and fat-soluble vitamins
As the amount of bile acids entering the gut decrease with increasing
cholestasis, patients can loose the ability to absorb all of the fat present in
their diet. This reduction in fat absorption, called malabsorption, occurs
because the bile acids are needed for the normal intestinal absorption of fat.
So, when advanced cholestasis prevents adequate amounts of bile acids from
reaching the small bowel, the absorption of dietary fat and of the vitamins A,
D, E and K is reduced. As a result, undigested fat passing into the large
intestine causes diarrhea, while continuing malabsorption of fat can lead to
weight loss and vitamin deficiencies. A laboratory measurement of the amount of
fat in the bowel movements can reveal whether the dietary fat is being absorbed
normally or not.
Vitamins A, D, E, and K, referred to collectively as the fat-soluble
vitamins, are absorbed from the gut in the same way that dietary fat is
absorbed. Therefore, deficiencies of these vitamins can occur in advanced
cholestasis. Also, bear in mind that some of the other conditions associated
with PBC, such as pancreatic insufficiency, celiac sprue, and scleroderma with
bacterial overgrowth, can also lead to malabsorption of fat and of the
fat-soluble vitamins. Prior to the development of jaundice, however,
deficiencies of vitamins A and E actually occur in only a minority of PBC
patients. Vitamin A deficiency causes decreased vision in the dark. Vitamin E
deficiency can cause abnormal skin sensations or muscular weakness due to its
effects on the nerves that extend from the spinal cord.
As already noted, deficiency of vitamin D results in osteomalacia (bones with
inadequate amounts of calcium deposited in them.) Deficiency of vitamin K
reduces the liver's production of blood clotting proteins and consequently,
causes a tendency to bleed easily. Also, the resulting deficiency of clotting
factors makes a blood test called the prothrombin time (blood clotting test) to
become abnormal. Prothrombin is a clotting factor that is produced in the liver
and needed for the normal clotting of blood. It is important to recognize that
the liver damage itself also can impair production of blood clotting factors and
cause easy bleeding and an abnormal prothrombin time.
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